1. Field of the Invention
This invention relates to power tuning a terminal of a bi-directional communications system operating with at hybrid fiber-coax plant by analyzing a power level and a signal level transmitted upstream from the terminal to a head end.
2. Description of Prior Art
Hybrid fiber-coax (HFC) plants have been used in cable television (CATV) communications systems. Conventional HFC systems often experience problems when transmitting signals in an upstream or reverse transmission direction. In conventional HFC systems, power levels can be controlled in a downstream direction by amplifying the signals at a particular location, such as at the head end or at a downstream amplifier. Because the number of amplifying stations maintained is at a relative minimum, manually tuning the amplifying stations may be practical and economical.
However, a greater number of signal generators exist when transmitting an upstream signal. For example, in a CATV system a remote terminal, such as a settop box or a "decoder", is located at each subscribers residence. Thus, the number of terminals is relatively large and it is difficult to manually power tune each terminal.
It is important to properly tune the terminals in a conventional HFC system. Weak signals may not be transmitted by a coax-to-fiber converter. Upstream signals which are too strong can overdrive the laser and either burn out the laser or transmit a distorted signal and thereby distort all signals regardless of the source.
Conventional power tuning methods are similar to power adjustment methods. A command signal is transmitted to the terminal with a message to either increase or decrease the terminal transmitter power level at the terminal. The terminal is then polled and, if a response signal is received, the received power level is measured. If the received power level remains incorrect, another adjustment signal is transmitted to increment the power level up or down, as necessary. According to conventional power tuning methods, such cycle continues until the received power level is either correctly adjusted or the iteration process is aborted.
If a terminal responds to the polling signal, the terminal returns its terminal transmitter power level, typically as an ordinal number. With such conventional HFC system, when the head end transmits a signal to adjust the terminal transmitter power level by one increment, a terminal transmitter power level number is transmitted as one increment greater, in the next polling signal. Once a maximum or a minimum terminal transmitter power level is reached, the terminal transmitter power level number remains at such value.
U.S. Pat. No. 4,512,033 teaches a remote level adjustment system for use in a multi-terminal communications system. Remote terminals transmit and receive signals through a network and also respond to a polling signal by transmitting signals with information from respective terminal sites. A master terminal has a program and a circuit for transmitting level-setting signals and a receiver measures the power level of reply signals from selected remote terminals, deciding whether to adjust the power level and for transmitting a level-setting adjustment signal.
U.S. Pat. No. 4,554,579 discloses a two-way CATV system in which multiple subscriber address codes are assigned to multiple subscriber terminals. Each subscriber terminal has a decoder which compares a unique address code of the subscriber terminal with a received subscriber address code. If the address codes match, an address match signal is generated from a multibit pulse coded downstream command signal for initiating various command functions, including power adjustment.
U.S. Pat. No. 5,586,121 teaches an asymmetric network communications system in which a network manager, such as a hybrid access system, effects transmission of packets of data on a forward or downstream channel to multiple downstream subscribers. Forward and return channels are located on the same or different communication medium, such as a cable television network, direct broadcast satellite network, television or radio RF broadcast network. The network manager handles or controls the forward and return communication to establish interactive full-duplex real-time network sessions between the host and a selected subscriber device.
In view of the conventional technology, there is an apparent need to upgrade head end software so that the head end or a controller can calculate and set a power level based upon data received through an upstream status signal transmitted by the terminal.